The invention pertains to a method and to an apparatus for controlling the brake system of a vehicle having an electrically controlled duty brake and an electrically controlled sustained action brake (e.g., a retarder), both of which are adjusted as a function of the driver's braking command.
A method and an apparatus of this type are known from, for example, U.S. Pat. No. 5,303,986. This patent describes a control for the brake system of a vehicle in which both the duty brakes and a sustained-action brake (e.g., retarder, some type of motor brake, etc.) are controlled electrically. As a function of the braking command derived from the actuation of the brake pedal and possibly as a function of the axle load of the vehicle, desired settings are formed both for the duty brake and also for the retarder to implement the braking command. The desired setting for the duty brake is a function of the difference between the braking command and the desired setting for the retarder. Because of the exclusive use of desired values to form the desired settings, this procedure can lead to unsatisfactory braking behavior. The desired setting for the retarder can differ significantly from the actual static value, because the achievable braking moment of the retarder depends on the retarder's operating status (e.g., a thermal overload in the case of a hydrodynamic retarder). Under dynamic operating conditions, furthermore, it can also lead to a delay in the increase in the braking action, which is perceived as unpleasant by the driver.